1. Field of the Invention
This invention relates to a linear motor.
2. Description of the Prior Art
Dynamoelectric motors are well known and generally include a bobbin about which is wound one or more field coils. Mounted within the bobbin is an armature which may be comprised of a core formed from a piece of soft iron, as shown in U.S. Pat. No. 3,728,654; or, it may be comprised of a plurality of permanent magnets, as shown in U.S. Pat. Nos. 3,022,400, 3,202,886 and 3,495,147; or the armature may be a combination of a core and a permanent magnet. The application of a direct current in one direction to the field coil generates a magnetic field which produces a force to drive the armature in a first direction until it is physically stopped and the reverse application of the direct current to the field coil will cause the armature to be driven in an opposite direction until it again hits a physical stop. One disadvantage of the motors described and shown in the above-identified patents is that each output shaft produces only one stroke for each energization and deenergization of its field coil. In other words, the armature does not return to its original position upon the deenergization of its field coil.
One of the problems with returning an armature to its original position is the precise positioning of the armature relative to the field coil thereby insuring that the length of each stroke is substantially the same. One proposed solution is offered in U.S. Pat. No. 3,549,917 wherein opposing springs are used to center or return an armature to its original position upon the deenergization of its field coil. Also, see U.S. Pat. No. 3,755,699 wherein flexible diaphragms are used to return a bobbin to its central position. However, the matching of the opposing springs or diaphragms to insure that they will always provide equal and opposite forces leaves much to be desired, both practically and economically.
U.S. Pat. No. 3,860,300 describes a control system including a plurality of permanent magnets made from samarium cobalt and a pair of electromagnets for repositioning a rotating shaft. The output of each electromagnet is controlled by a circuit containing a differential amplifier. See also U.S. Pat. No. 3,874,750 wherein a permanent magnet thrust bearing system is used to locate a rotatable shaft relative to a fixed number. However, neither of these systems is related to an environment wherein a field coil is energized to move an armature axially in order to provide an output for driving a member and, when deenergized, is automatically returned to its original position.